Currently, the technology of CDMA2000 Single Carrier Evolution-Data Optimized (1xEV-DO) uses a single carrier to transmit data traffic. With the development of communication technologies, a higher data transmission rate is desired. The Third Generation Partnership Project 2 (3GPP2) proposes a new air interface evolution plan. In the first phase of the plan, a great increase in air interface data transmission rate is enabled through using Multiple Carrier EV-DO (NxEV-DO). It is required that the forward data transmission rate is no lower than N times of 3.1 Mbps and the reverse data transmission rate is no lower than N times of 1.8 Mbps, in which N is the number of carriers used by an Access Network (AN) or an Access Terminal (AT). An NxEV-DO system also has to enable dynamic and independent allocation and deletion of forward carriers and reverse carriers through coordinated operations of the AN and the AT, but the number of the forward carriers and the number of the reverse carriers are not required to be symmetric.
In a 1xEV-DO system, an operation status of a forward traffic channel may be divided into a variable-rate status and a fixed-rate status. In the variable-rate status, the AT notifies the AN of the AT's desired service sector and data rate through transmitting a Data Rate Control (DRC) channel. When the AN cannot demodulate the DRC channel due to degradation of reverse carrier links or other reasons, the AN may not transmit a forward traffic channel to the AT. At this time, the AN notifies the AT that the AN may not receive the DRC channel correctly, and the AT notifies, through a FixedModeEnable (Fixed Mode Enable) message, the AN of information about the sector from which AT expects to receive a forward traffic channel, and also a fixed data rate at which AT expects to receive the forward traffic channel. The format of the FixedModeEnable message in the 1x-EV-DO system is as illustrated in Table 1.
TABLE 1FieldLength (in bit)MessageID8TCAMessageSequence8DRCCover3DRCValue4EndTime16Reserved1
In Table 1, the field MessageID (Message Identifier) is adapted to identify a FixedModeEnable message, and is set as 0×00 by the AT. The field TCAMessageSequence (Traffic Channel Assignment Message Sequence) is set by the AT as a value of the field MessageSequence in a TCA message. The field DRCCover (Data Rate Control Cover) is set by the AT to the DRC cover associated with the sector in AT's Active Set from which the AT expects to receive packets on the forward traffic channel at a fixed rate. The field DRCValue (Data Rate Control Value) is set by the AT as a value of a fixed rate. The field EndTime is set by the AT as a time at which the AT intends to end a fixed-rate status. The field Reserved is set by the AT as 0, and is ignored by the AN.
Portions appended to a FixedModeEnable message are as illustrated in Table 2.
TABLE 2ChannelRTCSLPBest EffortAddressingUnicastingPriority40
The information in Table 2 shows the portions that are appended to any message. The Channel indicates a channel over which a FixedModeEnable message may be transmitted, for instance, a Reverse Traffic Channel (RTC). The Addressing indicates that a FixedModeEnable message is transmitted in a unicast way but not in a broadcast or multicast way. The SLP indicates that a FixedModeEnable message is transmitted in a best-effort way. In the best-effort way, a FixedModeEnable message is transmitted only once and may be lost during the transmission. The Priority indicates a priority in which a FixedModeEnable message is transmitted, and the smaller the number of the Priority is, the higher the priority is.
In a multiple carrier EV-DO system, the operation status of a forward traffic channel may also be divided into a variable-rate status and a fixed-rate status. In the 1xEV-DO system, a sector is provided with only one forward carrier link; while in the multiple carrier EV-DO system, a sector may be provided with a plurality of forward carrier links. In the variable-rate status, an AN transmits a forward traffic channel at a variable rate, with the value of the rate designated by DRC. In the fixed-rate status, the AN transmits a forward traffic channel(s) to the AT at a fixed rate from one or more specific sectors. If the AT needs to transform from the variable-rate status to the fixed-rate status, the AT transmits a FixedModeEnable message to the AN.
A FixedModeEnable message in the current multiple carrier EV-DO system has a format as illustrated in Table 3.
TABLE 3FieldLength (in bit)MessageID8TCAMessageSequence8NumForwardChannels5NumForwardChannel occurrences of the following record:DRCCover3DRCValue4EndTime16Reserved1
The format of the FixedModeEnable message in Table 3 is substantially the same as the format of the FixedModeEnable message in Table 1 except for an additional field NumForwardChannels (the number of forward carriers), and the other fields and their definitions are identical. The field DRCCover identifies a sector from which the AT intends to receive a forward carrier link. The AT sets the field NumForwardChannels as the number of sectors from which the AT intends to receive forward traffic channels. The fields DRCValue and DRCCover occur for NumForwardChannels times.
In the multiple carrier EV-DO system, because Data Rate Control (DRC) channels may be transmitted over a plurality of reverse carrier links, there is a need for the AT to intend to receive a forward traffic channel(s) at a fixed rate from a specific forward carrier link(s) of a sector. However, the current format of the FixedModeEnable message may result in that all forward carrier links of a specific sector(s) transmit a forward traffic channel(s) at the same fixed rate.
Obviously, the above method for transmitting a forward traffic channel(s) in a fixed-rate status may not satisfy the need for the AT to receive a forward traffic channel(s) at a fixed rate from a specific forward carrier link(s) of a specific sector(s).